The present invention relates to an improved magnetic encoder and a method for producing the same, and more particularly relates to production of a peripheral-magnetization type magnetic encoder adapted for detection of angular displacement, linear displacement and displacement speed of a mobile body in a control system for robots and NC equipments.
A peripheral-magnetization type magnetic encoder in general includes a rotary spindle coupled to a control system. The rotary spindle is mounted to a housing via bearings partly projecting outwards. A magnetic recording medium is coaxially mounted to the projecting section of the rotary spindle and a magnetized pattern is formed on the periphery of the magnetic recording medium. A magnetic detection head is arranged whilst facing the magnetized pattern on the magnetic recording medium with a prescribed clearance.
As the recording medium rotates with the rotary spindle, magnetic field applied to the detection head changes depending upon the magnetized pattern on the recording medium and, in response to such change in the magnetic field, the detection head generates a series of output signals representative of the magnetized pattern on the recording speed for detection of angular displacement, linear displacement or displacement speed of a mobile object in the control system connected to the rotary spindle.
For correct detection of the displacement or displacement speed, the clearance between the detection head and the magnetized pattern on the recording medium has to be maintained as constant as possible during rotation of the recording medium. In practice, however, the clearance inevitably fluctuate due to production errors of the rotary spindle and the recording medium, coupling error between the spindle and the recording medium and/or production error of the bearings interposed between the rotary spindle and the housing. All these troubles are believed to be caused by the above-described double mounting system in which the magnetic recording medium is mounted to the housing via the rotary spindle and the rotary spindle is mounted to the housing via the bearings.